1. Field of Invention
The present invention relates to a wear detection probe for a braking member, particularly but not exclusively a braking member of a vehicle braking system, and further relates to a braking member having such a wear detection probe mounted thereon and to a brake including such a braking member.
2. Description of Related Art
A wear detection probe for detecting the degree of wear of a braking pad of a vehicle disclosed in U.S. Pat. No. 5,833,033 has an electrical detection wire folded in the shape of a xe2x80x9cUxe2x80x9d embedded in a holder made of resin. The wear detection probe is installed on a braking pad, with the apex at the folded portion of the wire exposed and opposed to a disk rotor and with two straight line portions of the wire extending from the folded portion parallel to the axis of the disk rotor. With the progress of the wear of the braking pad, the folded portion of the detection electric wire contacts the disk rotor and is abraded. When the wear of the braking pad reaches its use limit, the folded portion is broken, enabling an electrical signal to be derived.
In the wear detection probe, the two straight line portions of the wire extend to the rear side of the braking pad (opposite to the location of the disk rotor) and are connected to an external wire breakage detection circuit. Depending on the kind of vehicle, a sufficient space for electrical wiring is not available at the rear side of the braking pad.
Thus, a wear detection probe 1 as shown in FIGS. 9 and 10 has been proposed but is not thought to have been publicly used. This wear detection probe 1 is installed on a braking pad 4, with two straight line portions 2Sa and 2Sb of an electrical detection wire 2 parallel with a surface 3a of a disk rotor 3 and with the one straight line portion 2Sa nearer to the disk rotor 3 than the other straight line portion 2Sb. By arranging the straight line portions 2S in this manner, the wire 2 is extended out of the holder 4 in the radial direction of the disk rotor 3.
In the wear detection probe 1, with the progress of the wear of the braking pad 4, the straight line portion 2Sa nearer to the disk rotor 3 contacts the disk rotor 3 and is abraded thereby. When the wear of the braking pad 4 reaches the limit of use, as shown in FIG. 10, the straight line portion 2Sa nearer to the disk rotor 3 is broken, which event is detected by a wear detection circuit.
However, in the wear detection probe 1 having the two straight line portions 2Sa and 2Sb parallel with the surface 3a of the disk rotor 3, when the radius of curvature of a folded portion 2R of the electric wire 2 is reduced, there is a risk that the electric wire 2 is broken at the folded portion 2R. Accordingly, to make the radius of curvature of the folded portion 2R comparatively large, it is necessary to space the two straight line portions 2Sa and 2Sb from each other at a large interval in a direction perpendicular to the surface 3a of the disk rotor 3, which causes the wear detection probe 1 to be large.
To make the wear detection probe 1 more compact, it is conceivable to arrange the two straight line portions such that the distances between them and the surface of the disk rotor are equal, so that both straight line portions are subject to abrasion by the disk rotor. However, this construction causes the hole containing the wire to become open in the shape of a groove while the wear detection probe 1 is being abraded. As a result, there is a possibility that the wire becomes loose so that the desired manner of breaking of the wire is not achieved.
Accordingly, it is an object of the present invention to provide a wear detection probe which is compact in a direction perpendicular to the surface of a disk rotor, and which enables reliable wear detection.
According to the present invention, there is provided a wear detection probe for the detection of wear of a braking member, which in use is mounted on the braking member and includes a holder having a folded detection wire in a wiring path. The detection wire has a folded portion and two straight portions each extending from the folded portion in a direction substantially parallel to a wear surface of the holder which is worn away in use. The folded portion of the detection wire is located at a position nearer to the wear surface of the holder than the straight portions.
As in the probe of U.S. Pat. No. 5,833,033, the folded part of the detection wire in the probe of the invention is abraded by contact between the wire and the surface of the rotor and broken when the degree of wear of the braking member reaches a predetermined limit of use, thereby enabling an electrical signal indicating the wire breakage to be obtained.
According to the invention in a second aspect, there is provided a braking member that includes a body having an outer surface which is worn away in use and a wear detection probe mounted on the body. The wear detection probe having a holder has a wiring path therein. The probe also has a folded detection wire held in the wiring path and has a folded portion and two straight portions each extending from the folded portion in a direction substantially parallel to the outer surface of the braking member. The folded portion of the detection wire is located at a position nearer than the straight portions to the outer surface of the braking member.
According to the invention in a third aspect there is provided a brake that includes a rotor having a flat braking surface and a braking member that has a body having an outer surface parallel to the braking surface which in operation is brought into contact with the braking surface to effect braking of the rotor. The outer surface of the braking member is worn away in use. The braking member includes a wear detection probe mounted thereon. The wear detection probe includes a holder that has a wiring path therein. The probe has a folded detection wire held in the wiring path and has a folded portion and two straight portions each extending from the folded portion in a direction substantially parallel to the braking surface of the rotor. The folded portion of the detection wire is located at a position nearer than the straight portions to the braking surface of the rotor.
Preferably, the distance from one straight line portion to the surface of the rotor is equal to the distance from the other straight line portion to the surface of the rotor, i.e., the straight line portions lie in one plane. Preferably the two straight line portions are parallel to each other.
In the present invention, the two straight line portions are so disposed that the distance from the folded portion to the surface of the rotor is less than the distance from the straight line portions to the surface of the rotor. Thus, even though the spacing between the straight line portions is widened to increase the radius of curvature of the folded portion, the dimension of the path of the wire in the direction perpendicular to the surface of the rotor can be minimized, and may be equal to or slightly more than the outer diameter of the wire. Thus a minimal space is necessary for forming the region in which the two straight line portions are wired.
If both the two straight line portions were abraded by the rotor before the folded portion was broken, there is a fear that the detection wire may become loose. However, in the invention the folded portion to be broken is nearer than the two straight line portions to the rotor. Accordingly, the folded portion can be broken without abrading the two straight line portions. To break the detection wire without any abrasion of the two straight line portions, the apex of the folded portion is preferably located at a position nearer than the two straight line portions to the rotor by a distance greater than or equal to the outer diameter of the detection wire. In this case, in the direction perpendicular to the surface of the rotor, the dimension of the space required for the two straight line portions and the folded portion may be merely twice as large as the outer diameter of the detection wire.